I just bought an old, beat up Hartke 3500. These have the dual pre-amp where you can blend the solid state pre-amp with a tube pre-amp to get the tone you want. The tube channel is completely dead, even after replacing the old tube with a fresh JJ/Tesla 12AX7. The solid state sounds so good that I still can use the amp, and I was able to buy it for chump change so it's not a complete disaster. Still, I wonder if there might be a cheap and easy fix to get the tube side working. I am on a tight budget right now and I don't know of a good repair shop in my area (Riverside-San Bernardino, So.Cal.) I would really appreciate any helpful advice. Thanks!!